Ion collector for use in plasma systems

ABSTRACT

An ion collector includes a plurality of segments and a plurality of integrators. The plurality of segments are physically separated from one another and spaced around a substrate support. Each of the segments includes a conductive element that is designed to conduct a current based on ions received from a plasma. Each of the plurality of integrators is coupled to a corresponding conductive element. Each of the plurality of integrators is designed to determine an ion distribution for a corresponding conductive element based, at least in part, on the current conducted at the corresponding conductive element. An example benefit of this embodiment includes the ability to determine how uniform the ion distribution is across a wafer being processed by the plasma.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. patent application Ser. No.14/850,623, titled “Ion Collector for Use in Plasma Systems,” filed Sep.10, 2015, the disclosure of which is incorporated by reference herein inits entirety.

BACKGROUND

Plasma systems are frequently used in the industry for performingvarious semiconductor manufacturing processes. Plasma systems have beenused to clean contamination from the surfaces of wafers, to depositmaterial layers, for etching, for ion implantation, and for plasmadoping just to name a few examples. For any given process step, hundredsof wafers may undergo the process in a given day. As such, any issues orproblems with the plasma system can have a significant impact on thenumber of good die per wafer.

Special detectors that measure the number of ions from the plasma(sometimes known as dosimeters) may be used to measure the plasma iondistribution during a process. The ion distribution may be monitored todetermine if the plasma system needs to be taken off-line forreadjustment.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A and 1B illustrate views of a wafer stage with an integrated ioncollector, in accordance with some embodiments.

FIG. 2 illustrates connections made to segments of a ion collector, inaccordance with some embodiments.

FIG. 3 illustrates a control system, in accordance with someembodiments.

FIGS. 4A-4C illustrate another wafer stage with an integrated ioncollector, in accordance with some embodiments.

FIG. 5 illustrates a control system, in accordance with someembodiments.

FIG. 6 illustrates an example method, in accordance with someembodiments.

FIG. 7 illustrates an example plasma chamber for use with someembodiments.

FIG. 8 illustrates an example method, in accordance with someembodiments.

FIGS. 9A-9B illustrate a processing step of an example finFET device, inaccordance with some embodiments.

FIGS. 10A-10B illustrate another processing step of an example finFETdevice, in accordance with some embodiments.

FIG. 11 illustrates another processing step of an example finFET device,in accordance with some embodiments.

FIG. 12 illustrates another processing step of an example finFET device,in accordance with some embodiments.

FIG. 13 illustrates an example finFET device, in accordance with someembodiments.

Embodiments of the present invention will be described with reference tothe accompanying drawings.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” etc., indicate that theembodiment described may include a particular feature, structure, orcharacteristic, but every embodiment may not necessarily include theparticular feature, structure, or characteristic. Moreover, such phrasesdo not necessarily refer to the same embodiment. Further, when aparticular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of oneskilled in the art to effect such feature, structure or characteristicin connection with other embodiments whether or not explicitlydescribed.

FIG. 1A illustrates a stage system 100, according to an embodiment. FIG.1B illustrates a cross section of stage system 100 taken across lineA′-A′. Stage system 100 includes a support 102 that is designed tosupport a wafer 104. Support 102 may comprise any material for use in alithographic system as would be known to a person skilled in the art.For example, a common material for support 102 is steel. Support 102 mayinclude a vacuum system for holding wafer 104 in place. In anotherexample, support 102 includes an electrostatic chuck to clamp wafer 104in place via an applied potential.

According to an embodiment, support 102 includes a series of trench-likeopenings around the outside of wafer 104. Each of the trench-likeopenings includes a segment 106 a-106 h of an ion collector. It shouldbe understood that description herein of segment 106 a may also apply toany other segment. Each segment 106 a-106 h may be physically separatedby a wall 108. Each segment may also be electrically isolated from oneanother via an insulating material or high-k dielectric material placedbetween the segments. The total number and arrangement of segments mayvary. For example, any number of segments may be arranged in a circularpattern as shown with each segment separated from one another via wall108. The arrangement of the segments is not limited to the circularpattern illustrated. For example, the segments may be arranged in anyshape or configuration as long as they are arranged outside of the edgeof wafer 104. The segments may be arranged as close as possible to theedge of wafer 104. In one example, segments 106 a-106 h are arrangedsuch that a distance between a given segment and its nearest twoneighboring segments is the same for each segment.

During a plasma process, ions generated from the plasma bombard wafer104 across its surface, and will also pass through each of thetrench-like openings and impinge upon each segment 106 a-106 h of an ioncollector. By measuring the total charge associated with the ions thatpass through each trench-like opening, information can be determinedregarding the plasma ion distribution at (or at least near) wafer 104.As used herein, the term “ion distribution” relates to the total chargeaccumulated across a given area (such as a given segment) due to theions impacting across the given area. The ion distribution increases ifthe total number of ions across the given area increases. Additionally,the ion distribution increases with increasing charge of each ion.

Because the ion collector incudes multiple segments 106 a-106 h that arephysically and/or electrically separated from one another, informationabout the uniformity of the plasma can also be determined. For example,segment 106 a is associated with a closest portion ‘A’ of wafer 104,while segment 106 b is associated with a closest portion ‘B’ of wafer104, and so forth. Since the ion distribution is individually measurableat each segment 106 a-106 h, the uniformity of the plasma process acrossthe surface of the wafer can be monitored. The ability to monitor thisuniformity becomes even more important as the size of wafer 104increases. For example, when using 450 mm or 18″ diameter wafers, anychanges to the plasma uniformity can have a significant impact on theyield of devices across such a large footprint. Additionally, asegmented ion collector design like the one illustrated in FIG. 1A canbe used with single wafer or multiple wafer systems to monitor theplasma uniformity. The plasma may be used to dope wafer 104 with avariety of elements, such as boron, phosphorus, arsenic, or germanium.

The edge of wafer 104 can be seen on support 102 in the cross sectionillustration of FIG. 1B. Support 102 has a trench-like opening throughwhich lies segment 106 a, according to an embodiment. The opening allowsions from plasma 108 to pass through and impinge upon a conductiveelement 112. The width of the opening may be tailored based on theapplication and the total number of ions that are expected to begenerated. For example, the width of the opening may be between 1 and 3mm, between 3 and 5 mm, or between 5 and 10 mm. Plasma 108 may begenerated from the ionization of a wide array of source gases such asargon, chlorofluorocarbons, helium, etc., depending on the application.The generation and physics of the plasma are not discussed in anyfurther detail in this application.

Conductive element 112 may be any metallic material that can conduct acurrent. Example conductive materials include copper, aluminum,stainless steel, carbon, and graphite. Conductive element 112 may be aFaraday cup, in that it is shaped like a cup with walls designed tocatch ions at various angles and also to catch stray charges that aregenerated when an ion hits conductive element 112 and is neutralized.The walls of the cup may be at right angles, as illustrated, or they maybe curved. Conductive element 112 may include an open area, the “cup”,that has a width w similar to the width of the opening above it asillustrated in FIG. 1B. In some embodiments, the walls of the cup mayhave a first depth d₁ that extends between about 25% to about 50% of thetotal depth d₂ of conductive element 112. In some other embodiments, thewalls of the cup may have a first depth d₁ that extends between about50% to about 75% of the total depth d₂ of conductive element 112. Thetotal depth d₂ of conductive element 112 may range anywhere betweenabout 10 mm and 100 mm. Note that all of the dimensions provided arepurely exemplary, and other dimensions could be used as well withoutdeviating from the scope or spirit of the embodiments described herein.

Conductive element 112 is provided as an element in a circuit such thata current 114 can be measured directly from conductive element 112. Themeasured current is related to both the number and charge of the ionsimpacting upon conductive element 112 in segment 106 a. According to anembodiment, a magnetic element 116 is included. A magnetic fieldgenerated from magnetic element 116 may help prevent secondary electronsfrom escaping away from conductive element 112.

The space between conductive element 112 and support 102 may be filledwith a material to hold conductive element 112 in place. The fillingmaterial would ideally be non-conductive, such as a polymer or epoxy. Inanother example, the space between conductive element 112 and support102 is mostly open space except for attachment points made betweenconductive element 112 and support 102 to hold conductive element 112 inplace.

Conductive element 112 is spaced some distance d₃ away from wafer 104,but is preferably close to wafer 104 to more accurately measureuniformity of the plasma ions across the surface of wafer 104. In someembodiments, conductive element 112 is spaced in a range from about 2 mmto about 5 mm from wafer 104. In some other embodiments, conductiveelement 112 is spaced in a range from about 5 mm to about 10 mm fromwafer 104. In some other embodiments, conductive element 112 is spacedin a range from about 10 mm to about 20 mm from wafer 104.

Embodiments of an ion collector described herein may be used during anyplasma process for the formation of a variety of semiconductor devices.Some example plasma processes include ion implantation, plasma etching,PECVD, PEALD, and epitaxial growth.

FIG. 2 illustrates a parallel circuit arrangement for connecting to eachion collector segment 106 a-106 h, according to an embodiment. Eachsegment 106 a-106 h is respectively electrically coupled with anintegrator 202 a-202 h. Each integrator 202 a-202 h may include variouspassive and/or active electrical components necessary for measuring acurrent based on the accumulated charge in the corresponding segment.For example, each of integrator 202 a-202 h may include an ammeter orgalvanometer, the operation of which would be understood to one skilledin the art. From the received current, each integrator 202 a-202 hdetermines an ion distribution based on the received current and thearea of the corresponding conductive element exposed to the ions. Assuch, each integrator 202 a-202 h may include processing circuitryand/or logic designed to make such a determination. Additionally, theion distribution information may be stored in registers or addressablememory associated with each integrator 202 a-202 h.

The determined ion distribution information may be provided from eachintegrator 202 a-202 h to a user via a user interface. For example, adisplay mounted to or otherwise electrically coupled with a plasmasystem may display graphically, or numerically, the ion distributioninformation from various locations around the wafer for the currentplasma process. In another embodiment, the ion distribution informationis passed along to a controller that provides automatic control ofvarious parameters of the plasma system to compensate for any determinednon-uniformity of the ion distribution across the wafer.

In another embodiment, a single integrator is used with a plurality ofinputs to receive the current from each segment 106 a-106 h. The singleintegrator may include processing circuitry and/or logic designed todetermine an ion distribution for each of the received currents, andprovide the ion distribution information across a plurality of outputs.

In an embodiment, the single integrator may use a single input andsingle output and use various time or frequency modulation techniques toreceive the different current values and provide the ion distributioninformation for multiple segments 106 a-106 h. For example, frequencydivision multiplexing may be performed to assign a different frequency(or phase) modulation to each signal received from each segment 106a-106 h, such that the various signals can be received at one integratorinput. Then, the signals may be demodulated to match which signal camefrom which segment.

FIG. 3 illustrates a control system 300 for correcting non uniformity ofthe ion distribution across a wafer, according to an embodiment.According to an embodiment, control system 300 may be used with thesegmented ion collector design illustrated in FIG. 1A. Control system300 includes a controller 302 that includes processing circuitry and/orlogic designed to receive ion distribution information from each ofintegrators 310 and use that information to control parameters of theplasma system to compensate for any non-uniform measurements in realtime. Various segments 308 may be arranged around a wafer stage tocollect the ions generated from a plasma. In an example, segments 308are arranged in a circular pattern around the chuck that holds a wafer,such as the pattern illustrated in FIG. 1A. The illustration of onlythree segments 308 is for example only, and it should be understood thatany number of segments 308 and corresponding integrators 310 may beused.

Controller 302 may be capable of shutting off the plasma source if thenon-uniformity is greater than a given threshold. This may be based onany number of possible comparisons. For example, and with reference toFIG. 1A, if segment 106 a is measuring an ion distribution that is twiceas high as the next highest ion distribution measurement, thencontroller 302 would shut off the plasma source and issue a warning oralert to the user that the system requires maintenance. The user couldalso be provided with information that includes specifically whichsegment registered the out-of-bounds measurement. In another example,controller 302 shuts off the plasma source and issues a warning or alertif a standard deviation among all ion distribution measurements ishigher than a given threshold. Other methods of comparing measurementsto determine a degree of uniformity would be understood to a personskilled in the art.

In other examples, controller 302 may just issue warnings about theplasma uniformity, but continue running the plasma process. Test wafersmay be used during the process of measuring the plasma ion distributionto ensure a uniform distribution before production wafers are used. Inthis scenario, there would not be a need to shut off the plasma systemwhen running a process on a test wafer.

In an embodiment, upon receipt of the ion distribution information fromvarious segments 308, controller 302 may adjust the bias voltage appliedto all of (or portions of) the wafer (or wafers) being processed in anattempt to correct the plasma uniformity in real time. Block 304represents the adjustment being made to the wafer bias potential. Thechange to the wafer bias changes the electric field strength around thewafer, which in turn affects how the ions interact with the wafersurface.

Alternatively, or additionally, upon receipt of the ion distributioninformation from various segments 308, controller 302 may adjustparameters of the plasma source to affect characteristics of the plasma.Block 306 represents the adjustment being made to the plasma source.Examples of plasma parameters to control include gas concentrations, gasflow rates, and E-field intensity. A multi-zone plasma system may becontrolled to affect the plasma over specific regions of the wafer. Forexample, and with reference to FIG. 1A, if segment 106 a measured an iondistribution that was higher than the ion distribution measurements fromthe neighboring segments, the multi-zone plasma system may be adjustedby controller 302 such that the ion concentration (or total ion charge)would change primarily over section ‘A’ of wafer 104. In anotherexample, the multi-zone plasma system may be adjusted by controller 302to affect the ion concentration over each section of wafer 104.

Controller 302 may compare the received ion distribution measurementsand determine that no change needs to be made to any of the plasmasystem parameters. For example, if the ion distribution measurements areall within a given threshold of one another, controller 302 may continueto monitor, but not take any action to change either the wafer biaspotential (block 304) or the plasma source parameters (block 306.)

FIG. 4A illustrates a stage system 400, according to another embodiment.Stage system 400 includes support 102 that is designed to support wafer104 similar to stage system 100. However, stage system 400 includes asingle continuous trench-like opening that includes a continuousconductive element 401 of an ion collector. Conductive element 401 has acontinuous closed shape, such as a circular shape arranged around awafer chuck on support 102 as illustrated. According to an embodiment,conductive element 401 is mostly protected from the plasma ions by acover 402, except for a window 404. As noted by the double-ended arrows,cover 402 may be designed to rotate such that window 404 correspondinglymoves across the closed shape of conductive element 401 in either aclockwise or counter-clockwise direction. In this way, a particular areaof conductive element 401 that receives ions from the plasma can becontrolled. Cover 402 may be any material that prevents the ions frompenetrating through a thickness of cover 402. Although only one window404 is illustrated, it should be understood that any number of windowsmay be used through cover 402. The multiple windows may be spaced apartequally around cover 402. Window 404 may be any size that, when rotatedat a given speed, provides a complete measurement of the plasma iondistribution around the edge of wafer 104. In some embodiments, window404 extends in a range from about 1% to about 5% of the totalcircumference of cover 402. In some other embodiments, window 404extends in a range from about 5% to about 10% of the total circumferenceof cover 402. In some other embodiments, window 404 extends in a rangefrom about 10% to about 15% of the total circumference of cover 402.

The rotation speed of cover 402 may be adjustable. In one example, therotation speed is adjusted based on a diameter of conductive element401. For larger ion collectors used with larger wafer sizes, the speedmay be increased to measure the area around the wafer faster throughwindow 404. The size of window 404 may also be increased to allow moreions to be collected, at the cost of a finer resolution. It would bewithin the knowledge of a person skilled in the art to design a size ofwindow 404 and set a speed of cover 402 to adequately measure iondistribution for a given application.

Cross sections taken across ‘A’ and ‘B’ are shown in FIGS. 4B and 4C,respectively. Cross section ‘A’ illustrates where ions can impinge uponconductive element 401 through window 404. Cross section ‘B’ illustratesa portion of conductive element 401 that is protected by cover 402, thuspreventing ions from reaching conductive element 401 in this area. Sinceconductive element 401 is one continuous shape, only a single electricalconnection needs to be made to conductive element 401 to receive thecurrent that conducts through conductive element 401. This current isgenerated from the ions that impinge upon conductive element 401 throughwindow 404. Although not illustrated, it should be understood thatconductive element 401 may also include a magnetic element such asmagnetic element 116 described with reference to FIG. 1B.

By moving window 404 along the closed shape of conductive element 401,an ion distribution can be determined for various areas around wafer104. As such, a position of window 404 is also monitored and comparedwith the measured current for a given time to determine what areacorresponds to the determined ion distribution. Monitoring of theposition of window 404 may be performed via the use of position sensorssuch as with IR sensors. Capacitive or electrostatic sensors may also beused by patterning electrodes on both cover 402 and support 102.

FIG. 5 illustrates a control system 500 for correcting non uniformity ofthe ion distribution across a wafer, according to an embodiment. Controlsystem 500 may be used with the continuous ion collector designillustrated in FIG. 4 . Control system 500 includes a controller 502that includes processing circuitry and/or logic designed to receive iondistribution information from integrator 510 and use that information tocontrol parameters of the plasma system to compensate for anynon-uniform measurements in real time. According to an embodiment,controller 502 also receives position data 512. Position data 512includes information about the location of window 404 as it moves overconductive element 401 of the continuous ion collector. Position data512 may be collected using any of the various techniques for monitoringthe location of window 404 mentioned previously. Position data 512 isthen received by controller 502 and is correlated with the iondistribution information received from integrator 510 to determine ageneral location where a given ion distribution is measured.Alternatively, if a rotation speed of cover 402 is controlled and known,then controller 502 may also correlate the received ion distributioninformation from integrator 510 with the time that it is received todetermine a general location where a given ion distribution is measured.

Controller 502 may be capable of shutting off the plasma source if thenon-uniformity is greater than a given threshold. This may be based onany number of possible comparisons. For example, if the received iondistribution information changes more than a threshold amount during thetime that window 404 makes one full revolution, then controller 502would shut off the plasma source and issue a warning or alert to theuser that the system requires maintenance. The user could also beprovided with information that includes specifically which arearegistered the highest or lowest ion distribution reading. Other methodsof comparing measurements to determine a degree of uniformity would beunderstood to a person skilled in the art.

In an embodiment, upon receipt of the ion distribution information fromintegrator 510, controller 502 may adjust the bias voltage applied toall of (or portions of) the wafer (or wafers) being processed in anattempt to correct the plasma uniformity in real time. Block 504represents the adjustment being made to the wafer bias potential. Thechange to the wafer bias changes the electric field strength around thewafer, which in turn affects how the ions interact with the wafersurface.

Alternatively, or additionally, upon receipt of the ion distributioninformation from integrator 510, controller 502 may adjust parameters ofthe plasma source to affect characteristics of the plasma. Block 506represents the adjustment being made to the plasma source. Examples ofplasma parameters to control include gas concentrations, gas flow rates,and E-field intensity. A multi-zone plasma system may be controlled toaffect the plasma over specific regions of the wafer. For example, ifthe ion distribution measurements show an abnormal reading (e.g., toohigh or too low) for a given area around the outside of wafer 104, thenthe multi-zone plasma system may be adjusted by controller 502 such thatthe ion concentration (or total ion charge) would change primarily overa section of wafer 104 nearest to the area where the abnormal readingwas received from. In another example, the multi-zone plasma system maybe adjusted by controller 502 to affect the ion concentration overvarious sections of wafer 104.

Controller 502 may continuously monitor the received ion distributionmeasurements and determine that no change needs to be made to any of theplasma system parameters. For example, if the ion distributionmeasurements continue to remain within a given threshold over time,controller 502 may continue to monitor, but not take any action tochange either the wafer bias potential (block 504) or the plasma sourceparameters (block 506.)

FIG. 6 illustrates a flowchart of a method 600, according to anembodiment. Method 600 may be performed by either ion collector designillustrated in FIG. 1A or FIG. 4 . Method 600 may be the steps of analgorithm executed by controller 302/502 in concert with integrator310/510. It should be understood that other steps not illustrated mayalso be performed without deviating from the scope or spirit of theembodiments described herein.

Method 600 starts at block 602 where the ion distribution is determinedfrom different locations around a wafer (or around a group of wafers),according to an embodiment. The ion distribution at different locationsmay be determined based on current measurements from various segments orbased on a current measurement from a continuous conductive element ofan ion collector where the ions only impact a controlled portion of thecontinuous conductive element. The ion distribution may be determined byan integrator that receives the current measurement(s) from theconductive element(s) of the ion collector.

At block 604, the ion distribution measurements may becompared/contrasted to estimate how uniform the ion distribution isacross the wafer, according to an embodiment. This comparison may beperformed by controller 302/502. The comparison may involve anymathematical technique used to compare different measurements as wouldbe understood to one skilled in the art. Some examples of measurementcomparisons were given above when describing FIGS. 3 and 5 .

At block 606, a determination is made whether the compared iondistribution measurements indicate that the uniformity of the iondistribution is too uneven across the wafer, according to an embodiment.For example, if the compared measurements indicate that the discrepancybetween various ion distribution measurements is greater than a giventhreshold, then the plasma system may be shut off at block 608. Thisthreshold may be set to a value that indicates that the plasma system istoo far out of its normal operating state to be adjusted in real time,and that it must be shut down to be serviced.

If the ion distribution is not determined to be too uneven (e.g., themeasurements are within a given threshold), method 600 continues toblock 610 where a determination is made if minor adjustments to thesystem parameters are required, according to an embodiment. Thisdetermination may be made based on a second threshold different from thethreshold used to determine if the plasma system needed to be shut down.For example, the ion distribution measurements may exhibit somenon-uniform behavior that isn't high enough to be greater than thethreshold at block 606, but is high enough to be greater than the secondthreshold at block 610. If the discrepancy between the ion distributionmeasurements is greater than the second threshold than the methodproceeds to block 612 where minor adjustments may be performed inreal-time while the plasma system is still operating. The minoradjustments may involve changing a bias voltage applied to the wafer ora wafer chuck holding the wafer. The minor adjustments may involveadjusting parameters of the plasma source to affect characteristics ofthe plasma.

If it is determined in block 610 that minor adjustments are not required(e.g., the ion distribution measurements exhibit good uniformity acrossthe wafer), then method 600 proceeds back to block 602 where iondistribution at different locations is continually monitored and method600 repeats. Additionally, after performing adjustments at block 612,method 600 returns to block 602 to continue monitoring the iondistribution at different locations.

FIG. 7 provides a simple block diagram depicting various components ofan example plasma chamber that may implement embodiments of the presentdisclosure. As shown, a reactor 700 includes a process chamber 724,which encloses other components of the reactor and serves to contain theplasma generated by a capacitor type system including a showerhead 714working in conjunction with a grounded heater block 720. Ahigh-frequency (HF) RF generator 702 and a low-frequency (LF) RFgenerator 704 may be connected to showerhead 714. An impedance matchingnetwork 706 may be included with either or both of HF generator 702 andLF generator 704. In an alternative embodiment, LF generator 704 isconnected to, or located below, a wafer stage 718. The power andfrequency supplied by HF generator 702 may be sufficient to generate aplasma from a process gas/vapor. In a typical process, the HF generatoris operated generally at frequencies in a range from about 2 MHz toabout 60 MHz. The power output may be about 3.3 kW. The LF generator isoperated generally at frequencies in a range from about 100 kHz to about800 kHz.

Within reactor 700, wafer stage 718 supports a substrate 716. Waferstage 718 may include a chuck, a fork, or lift pins to hold and transfersubstrate 716 during and between the deposition and/or plasma treatmentreactions. The chuck may be an electrostatic chuck, a mechanical chuckor various other types of chuck as are available for use in the industryand/or research. Wafer stage 718 may be functionally coupled withgrounded heater block 720 for heating substrate 716 to a desiredtemperature. Generally, substrate 716 is maintained at a temperature ina range from about 25° C. to about 500° C.

Wafer stage 719 may be arranged to deliver high voltage pulses tosubstrate 716 during a plasma process. The pulses may be in a range fromabout −0.2 kV to about −10 kV (for directing positive ions towardssubstrate 716, negative ions would use positive pulses), from about 20microseconds to about 100 microseconds long, and at a frequency in arange from about 0.5 kHz to about 10 kHz.

According to an embodiment, wafer stage 718 includes segments of an ioncollector (such as segments 106 a-106 h illustrated in FIG. 1A) arrangedaround substrate 716. According to another embodiment, wafer stage 718includes an ion collector having a cover (such as conductive element 401and cover 402 illustrated in FIG. 4 ) arranged around substrate 716.

Process gases/vapors may be introduced via inlet 712. Multiple sourcegas lines 710 are connected to manifold 708. The gases/vapors may bepremixed or not in the manifold. Appropriate valving and mass flowcontrol mechanisms are employed to ensure that the correct gases aredelivered during the deposition and plasma treatment phases of theprocess. In case the chemical precursor(s) is delivered in the liquidform, liquid flow control mechanisms are employed. The liquid is thenvaporized and mixed with other process gases during its transportationin a manifold heated above its vaporization point before reaching thedeposition chamber.

Process gases exit chamber 724 via an outlet 722. A vacuum pump 726(e.g., a one or two stage mechanical dry pump and/or a turbomolecularpump) typically draws process gases out and maintains a suitably lowpressure within reactor 700 by a close loop controlled flow restrictiondevice, such as a throttle valve or a pendulum valve. Pressures inreaction chamber 724 may be maintained in a range from about 0.1 Torr toabout 30 Torr.

In certain embodiments, a system controller 728 is employed to controlprocess conditions and other process operations of reactor 700.Controller 728 will typically include one or more memory devices and oneor more processors. The processor may include a CPU or computer, analogand/or digital input/output connections, stepper motor controllerboards, etc.

Controller 728 may control all of the activities of reactor 700.Controller 728 may execute system control software including sets ofinstructions for controlling the timing of the processing operations,frequency and power of operations of LF generator 702 and HF generator704, flow rates and temperatures of precursors and inert gases and theirrelative mixing, temperature of the heater block 720, pressure of thechamber, and other parameters of a particular process. According to anembodiment, controller 728 may also receive as an input a signal fromsegments of an ion collector arranged around substrate 716, and use thatreceived signal to control various processes of reactor 700.

FIG. 8 illustrates a flowchart of a method 800, according to anembodiment. Method 800 may be performed using a plasma system (such asplasma chamber 1 in FIG. 7 ) that includes either ion collector designillustrated in FIG. 1A or FIG. 4 . It should be understood that othersteps not illustrated may also be performed without deviating from thescope or spirit of the embodiments described herein.

Method 800 starts at block 802 where a substrate is disposed on asupport within a plasma chamber. For example, a substrate may be placedon puck 810 from FIG. 7 .

At block 804, a voltage bias is applied to the substrate via the supportit is placed upon. This voltage bias may be a DC voltage applied to forman electric field within the plasma chamber to direct ions towards thesubstrate. The voltage bias may be applied via a controller thatreceives input from a user or is autonomously generated.

At block 806 a plasma is generated within the plasma chamber. The plasmamay be generated from any number of ways as would be understood by aperson skilled in the art. For example, the plasma may be generated byflowing in one or more gases that are ionized via RF energy. Thefrequency and amplitude of the RF energy may be changed to affect theproperties of the plasma. Similarly, the gas(es) used, or flowrate ofthe gas(es) into the plasma chamber, may be changed to affect theproperties of the plasma.

At block 808, the ions from the plasma are directed towards thesubstrate on the support. How fast the ions are driven towards thesubstrate may depend on the voltage bias applied to the substrate.

At block 810, at least some of the ions are collected at a plurality ofsegments around the support. For example, each segment of the pluralityof segments includes a conductive element that is designed to conduct acurrent based on the ions received from the plasma. The plurality ofsegments are each spaced some distance apart on the support around wherethe substrate is placed (like the example illustrated in FIG. 1A.) Inanother embodiment, the ions are collected at a single conductiveelement through a window that rotates around the conductive element asdescribed in more detail in FIG. 4 and its accompanying description.

At block 812, the ion distribution is determined based on the receivedcurrent from each of the plurality of conductive elements. The iondistribution measurements may be compared/contrasted to estimate howuniform the ion distribution is across the wafer, according to anembodiment. This comparison may be performed by, for example, controller302/502. The comparison may involve any mathematical technique used tocompare different measurements as would be understood to one skilled inthe art. Some examples of measurement comparisons were given above whendescribing FIGS. 3 and 5 .

The plasma ion distribution may be monitored during various fabricationsteps of making a finFET. Some example process steps of a finFET deviceis shown in FIGS. 9-12 . These steps provide a lightly doped drain (LDD)plasma process, according to an embodiment. It should be understood thatthe finFET device illustrated in FIGS. 9-12 is just an example of such adevice with certain features omitted for clarity. Other fabricationsteps and material layers may be included in the finFET device.

FIG. 9A is a side view in the X-Y plane of three fins 904 of a finFETdevice on a substrate 902, in accordance with some embodiments. FIG. 9Bprovides a cross-section view in the Y-Z plane of one fin through thedotted line illustrated in FIG. 9A, in accordance with some embodiments.Each finFET device includes a semiconductor fin 904 having a dielectriclayer 906 and a gate layer 908. Semiconductor fin 904 and substrate 902are commonly silicon, though other semiconducting materials such asgallium arsenide or indium phosphide may be used as well. Exampledielectric layers include silicon dioxide, nitride, and low-K dielectricmaterials. Dielectric layer 906 may comprise a stack of insulatingmaterial layers. Gate layer 908 is commonly doped polysilicon, but itmay also be a metal such as copper, gold, aluminum, or a metal alloy.Gate layer 908 may comprise a stack of conductive material layers. Insome embodiments, each fin 904 includes isolation region 905 to separatethe source/drain regions of adjacent fins. Isolation region 905 may besilicon trench isolation (STI) using an insulating material such as, forexample, silicon dioxide.

Gate layer 908 is polysilicon, according to an embodiment. Thepatterning of the polysilicon layer may be performed by using a hardmask including a silicon nitride layer and an oxide layer. Dielectriclayer 906 may be silicon oxide formed by CVD, PVD, ALD, e-beamevaporation, or other suitable process. In some embodiments, dielectriclayer 906 may include one or more layers of silicon oxide, siliconnitride, silicon oxy-nitride, or high-k dielectric materials. High-kdielectric materials may comprise metal oxides. Examples of metal oxidesused for high-k dielectrics include oxides of Li, Be, Mg, Ca, Sr, Sc, Y,Zr, Hf, Al, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu,and/or mixtures thereof. In some embodiments, a thickness of dielectriclayer 906 is in the range of about 1 nm to about 5 nm. In someembodiments, dielectric layer 906 may include an interfacial layer madeof silicon dioxide. In some embodiments, dielectric layer 906 maycomprise a single layer or multilayer structure. Gate layer 908 may bedoped poly-silicon with uniform or non-uniform doping. In somealternative embodiments, gate layer 908 includes a metal such as Al, Cu,W, Ti, Ta, TiN, TiAl, TiAlN, TaN, NiSi, CoSi, other conductive materialswith a work function compatible with the substrate material, orcombinations thereof. Gate layer 908 may be formed using a suitableprocess such as ALD, CVD, PVD, plating, or combinations thereof. Thewidth of gate layer 908 (in the Z direction) is in the range of about 30nm to about 60 nm in some embodiments.

The finFET device includes an interface 903 between fins 904 andsubstrate 902, an interface 901 between dielectric layer 906 andsubstrate 902, an interface 911 between dielectric layer 906 and fin 904on the top surface of fin 904, and an interface 913 along a top surfaceof fin 904. In an embodiment, interface 903 is coplanar with interface901. In other embodiments, interface 903 is either above or belowinterface 901. In an embodiment, interface 911 is coplanar withinterface 913. In other embodiments, interface 911 is either above orbelow interface 913.

FIGS. 10A and 10B illustrate a first plasma doping process using plasma1002, according to an embodiment. Plasma doping has an advantage ofbeing able to get between the fins to more easily to provide a conformaldoping profile. In one embodiment, the plasma includes an arsenic gas(AsH₃) to provide n-type dopants to the fins. Another doping gas exampleis B₂H₆ (for providing p-type dopants). The plasma is also commonlymixed with an inert gas such as helium, xenon, or argon. This firstdoping step provides a first concentration of dopants represented byregion 1004 in semiconductor fins 904. As can be seen in FIG. 10B, dopedregion 1004 extends into fin 904 at a depth d₄. In an embodiment, thedepth d₄ may be in a range from about 1 nm to about 10 nm. In anotherembodiment, the depth d₄ may be in a range from about 10 nm to about 50nm. The uniformity of this doping step across the wafer is important toreduce variation in device performance. The uniformity of the plasmadoping step may be monitored using any of the ion collector embodimentsdescribed herein.

FIG. 11 illustrates the cross-section view of the finFET device withpatterned spacers 1102 formed after the first doping step, according toan embodiment. Spacers 1102 maybe formed from nitride or silicondioxide, though other materials are possible as well. Spacers 1102 maybe formed via an etch-back technique where the material layer isdeposited and then etched such that the material only remains on thesidewalls of structures.

Gate structure 910 includes gate layer 908 patterned over dielectriclayer 906, with spacers 1102 patterned along the sidewalls of the stackincluding both gate layer 908 and dielectric layer 906. In someembodiments, gate layer 908 is used as a hard mask for etchingdielectric layer 906.

FIG. 12 illustrates the cross-section view of the finFET device havingpatterned spacers 1102 during a second plasma doping step using plasma1202, according to an embodiment. The second plasma gas provides ahigher concentration of dopants to doped region 1204. Spacers 1102protect the lighter doped region 1004 during the second plasma dopingstep. The second plasma doping step causes dopants to extend at a depthd₅ into fin 904. In an embodiment, the depth d₅ may be in a range fromabout 5 nm to about 15 nm. In another embodiment, the depth d₅ may be ina range from about 15 nm to about 55 nm. The uniformity of this dopingstep across the wafer is important to reduce variation in deviceperformance. The uniformity of the plasma doping step may be monitoredusing any of the ion collector embodiments described herein.

FIG. 13 illustrates a finFET device having a different gate structure910′, according to another embodiment. Gate structure 910′ includes gatelayer 908′ and dielectric layer 906′, which are similar to gate layer908 and dielectric layer 906 illustrated with reference to FIG. 9B. Gatestructure 910′ also includes one or more work function layers 907disposed between gate layer 908′ and dielectric layer 906′.

In the finFET device illustrated in FIG. 13 , interface 913 at the topsurface of fin 904, and not under dielectric layer 906′, is higher thaninterface 903 between dielectric layer 906′ and fin 904, according to anembodiment. Interface 901 between isolation region 905 and substrate 902is higher than interface 903 between fin 904 and substrate 902,according to an embodiment.

Example Embodiments and Benefits

In various embodiments, an ion collector includes a plurality ofsegments and a plurality of integrators. The plurality of segments arephysically separated from one another and spaced around a substratesupport. Each of the segments includes a conductive element that isdesigned to conduct a current based on ions received from a plasma. Eachof the plurality of integrators is coupled to a corresponding conductiveelement. Each of the plurality of integrators is designed to determinean ion distribution for a corresponding conductive element based, atleast in part, on the current conducted at the corresponding conductiveelement. An example benefit of this embodiment includes the ability todetermine how uniform the ion distribution is across a wafer beingprocessed by the plasma.

Various embodiments the ion collector described herein may be usedduring a plasma doping process, such as the plasma doping processillustrated in FIGS. 9-12 . The uniformity across one or more wafersduring these plasma doping steps may be measured by determining the iondistribution collected at various segments of an ion collector spacedaround the one or more wafers. The embodiments of the ion collectordescribed herein increase the accuracy of the uniformity measurementacross the one or more wafers, resulting in better system control and ahigher device yield.

In various embodiments, an ion collector includes a conductive elementhaving a closed shape arranged on a substrate support, wherein theconductive element is configured to generate a current based on ionsreceived from a plasma. The ion collector also includes a cover disposedover the conductive element. The cover has an opening over one part ofthe conductive element, and the cover is designed to move across theclosed shape of the conductive element such that the openingcorrespondingly moves across the closed shape of the conductive element.The ion collector also includes an integrator coupled to the conductiveelement. The integrator determines an ion distribution for a portion ofthe conductive element exposed to the plasma under the opening in thecover. The ion distribution is determined, at least in part, based on acurrent generated at the conductive element. An example benefit of thisembodiment includes the ability to determine how uniform the iondistribution is across a wafer being processed by the plasma.

In some embodiments, an ion distribution is measured at a plurality ofindividually measurable locations around a substrate support. Themeasured ion distribution is compared between at least two of theindividually measurable locations and the parameters of the plasmasystem are adjusted if a difference between the measured plasma energyis greater than a threshold. An example benefit of this embodimentincludes the ability to determine how uniform the ion distribution isacross a wafer being processed by the plasma.

In some embodiments, a substrate is disposed on a support within aplasma chamber. A bias voltage is applied to the substrate, and a plasmasystem is used to generate a plasma within the plasma chamber. The ionsare directed from the plasma towards the substrate. The method includescollecting at least some of the ions at a plurality of segmentsphysically separated from one another and spaced around the support,wherein each segment of the plurality of segments includes a conductiveelement configured to conduct a current based on the ions received fromthe plasma. The method further includes determining an ion distributionfor a corresponding conductive element based, at least in part, on thecurrent conducted at the corresponding conductive element.

It is to be appreciated that the Detailed Description section, and notthe Abstract section, is intended to be used to interpret the claims.The Abstract section may set forth one or more but not all exemplaryembodiments of the present invention as contemplated by the inventor(s),and thus, is not intended to limit the present invention and theappended claims in any way.

Embodiments of the present invention have been described above with theaid of functional building blocks illustrating the implementation ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. An ion collector, comprising: a plurality ofconductive elements physically separated from one another and radiallyarranged around a substrate, wherein each conductive element of theplurality of conductive elements is disposed at a same radial distancefrom the substrate and is configured to conduct a current based on ionsreceived from a plasma; a plurality of integrators, wherein eachintegrator of the plurality of integrators is coupled to a respectiveconductive element and is configured to determine an ion distributionfor the respective conductive element based on the current conducted atthe respective conductive element; and a controller coupled to theplurality of integrators, wherein the controller is configured todetermine a difference between the ion distribution from at least twoconductive elements and adjust a parameter controlling the iondistribution according to a comparison between the difference and athreshold voltage.
 2. The ion collector of claim 1, wherein a distancebetween each of the conductive elements and its two nearest neighboringconductive elements is the same for each of the conductive elements. 3.The ion collector of claim 1, further comprising a plurality of magneticelements, wherein each magnetic element of the plurality of magneticelements is coupled to a respective conductive element.
 4. The ioncollector of claim 1, wherein the controller is configured to receivethe ion distribution from each of the plurality of integrators.
 5. Theion collector of claim 1, wherein the parameter controlling the iondistribution is a bias voltage of the substrate.
 6. The ion collector ofclaim 1, wherein the parameter controlling the ion distribution is abias voltage to a portion of the substrate.
 7. The ion collector ofclaim 1, wherein the controller is further configured to shut off theplasma if the difference is greater than the threshold voltage by agiven amount.
 8. A plasma control system, comprising: a plurality ofarc-shaped segments radially arranged around a substrate, wherein eacharc-shaped segment of the plurality of arc-shaped segments is disposedat a same radial distance from the substrate; a plurality ofintegrators, wherein each integrator of the plurality of integrators iscoupled to a respective arc-shaped segment and is configured todetermine an ion distribution for the respective arc-shaped segment,wherein the ion distribution at each of the arc-shaped segmentscorresponds to an ion distribution on a respective circular sectorregion of the substrate; and a controller coupled to the plurality ofintegrators, wherein the controller is configured to determine adifference between the ion distribution from at least two arc-shapedsegments and selectively apply a bias voltage to at least one of thecircular section regions.
 9. The plasma control system of claim 8,wherein each of the arc-shaped segments is disposed adjacent to therespective circular sector region of the substrate and a total number ofthe arc-shaped segments is equal to a total number of the circularsector regions.
 10. The plasma control system of claim 8, wherein adistance between each of the arc-shaped segments and its two nearestneighboring arc-shaped segments is the same for each of the arc-shapedsegments.
 11. The plasma control system of claim 8, wherein thearc-shaped segments are electrically isolated from each other.
 12. Theplasma control system of claim 8, further comprising a plurality ofmagnetic elements, wherein each magnetic element of the plurality′ ofmagnetic elements is coupled to a respective arc-shaped segments. 13.The plasma control system of claim 8, wherein the controller isconfigured to receive the ion distribution from each of the plurality ofintegrators.
 14. The plasma control system of claim 8, wherein thecontroller is configured to adjust the bias voltage in response to thedifference being greater than the threshold voltage.
 15. A system,comprising: conductive elements radially arranged around a substrate,wherein each of the conductive elements is disposed at a same radialdistance from the substrate and is configured to conduct a current basedon ions received from a plasma; integrators coupled to the conductiveelements and configured to determine an ion distribution at each of theconductive elements; and a controller coupled to the integrators andconfigured to: determine a difference between the ion distribution fromat least two of the conductive elements at the same radial distance fromthe substrate; compare the difference with a threshold voltage; andselectively adjust a bias voltage applied to a portion of the substratein response to the difference being greater than the threshold voltageto correct a non-uniformity of the ion distribution across thesubstrate.
 16. The system of claim 15, wherein the controller is furtherconfigured to selectively adjust the bias voltage applied to the portionof the substrate in real time to correct a non-uniformity of the iondistribution across the substrate.
 17. The system of claim 15, wherein adistance between each of the conductive elements and its two nearestneighboring conductive elements is the same for each of the conductiveelements.
 18. The system of claim 15, wherein the conductive elementsare electrically isolated from each other.
 19. The system of claim 15,wherein each of the conductive elements is disposed at a distance ofabout 2 mm to about 5 mm away from an edge of the substrate to measureuniformity of the ion distribution across the substrate.
 20. The systemof claim 15, wherein the controller is further configured to adjust oneor more parameters of the plasma.